[Prospective study on the relationship between treatment duration of antithyroid drug and remission rate of Graves' disease].

OBJECTIVE

To compare the potential benefits of 36-month treatment with 6- and 18-month treatment of antithyroid drug in patients with hyperthyroidism due to Graves' disease (GD).

METHODS

183 GD patients were studied prospectively. All patients received methimazole (MMI) at decreasing doses for 6, 18 or 36 months. The relapse rates 18 months after MMI withdrawal were compared between the three therapy groups.

RESULTS

The relapse rate 18 months after the discontinuation of treatment was higher in patients treated for 6 months than in those treated for 18 or 36 months. There was no significant difference between 18-month and 36-month treatment groups. At the end of therapy, serum thyroid stimulating antibody (TSAB) and TSH receptor antibody (TRAB) titers were greater in patents treated for 6 months (320 +/- 191 for TSAB and 8.72 +/- 5.23 for TRAB) and 18 months (165 +/- 87 and 4.55 +/- 4.17) than in those treated for 36 months (126 +/- 77 and 2.19 +/- 2.64), but no statistical difference was found between the three groups before MMI treatment. TSAB and TRAB titers were higher in patients who relapsed after discontinuation of MMI (287 +/- 94 and 6.14 +/- 2.37, respectively) compared with those who remained euthyroid through the 18-month follow-up period (144 +/- 61 and 1.97 +/- 1.06).

CONCLUSIONS

Negative TSAB or TRAB at the end of antithyroid therapy is a good indicator for a long-term remission after treatment withdrawal. However, treatment duration greater than 18 months does not improve remission rate of GD.